The present invention relates to an aperture plate and a method for manufacturing the same, and more particularly to an aperture plate suitable for serving as a stencil mask for cell projection lithography and a method manufacturing the aperture plate.
In manufacturing a semiconductor device such as an LSI, an electron-beam lithography system is used to form very fine patterns. An Mo plate is hitherto used for an aperture plate (i.e., transfer or stencil mask) for writing patterns. To improve the throughput, a method of using a stencil mask made of Si having a high forming accuracy for the cell projection lithography method is proposed in Japanese Patent Laid-Open No. 81750/1985, Japanese Patent Laid-Open No. 76216/1990, and Japanese Patent Laid-Open No. 243118/1992.
The following is the description of a flow chart for manufacturing an Si stencil mask proposed in them. A silicon nitride film is formed on one surface of a single-crystalline silicon substrate to remove the silicon nitride film at a portion corresponding to the opening of an aperture plate through etching. A silicon nitride film is formed on the other surface of the substrate and a Ti thin film and an Au thin film are formed in order on the silicon nitride film. A pattern complemental with a mask is formed on the Au thin film with resist, an electron beam absorbing layer is formed by means of Au plating, and the resist is removed. The Au thin film and Ti thin film at the opening of the electron beam absorbing layer are removed by ion etching until the silicon nitride film is exposed and thereafter the exposed portion of the single-crystalline silicon substrate is anisotropically etched by using the silicon nitride film as a protective mask.
Moreover, a stencil mask pattern is formed on one surface of a laminated single-crystalline silicon substrate, and thereafter a pattern facing the stencil mask pattern is opened to form the substrate into chips by dicing. An Si.sub.3 N.sub.4 film is used to protect the surface stencil mask pattern and mask the opening. Then, the chips are bonded to a glass plate by wax to protect the stencil mask pattern portion on the surface. Then, the chips are put in a KOH aqueous solution (at 75.degree. C.) and anisotropically etched up to a predetermined depth (up to the depth of an oxide film) and washed with water, and then organically washed and separated from the glass plate. A metallic film such as an Au film is formed on the pattern surface to finish the chips.
Moreover, the above Japanese Patent Laid-Open No. 76216/1990 describes a structure in which a thick rib is formed on a stencil mask made of Si. Furthermore, the Japanese Patent Laid-Open No. 243118/1992 discloses a constitution in which an antistatic film is formed.
Thus, a plurality of same stencil masks are formed on the single-crystalline silicon substrate. In the prior art, stencil masks are separated by means of dicing (cutting with a dicing saw).
The existing Si stencil mask producing method has the following problems because a method is used in which stencil masks are diced and separated into chips and the chips are protected by wax. That is, because Si is cut by a dicing saw and separated into chips, Si chips attach to stencil masks. Even if the stencil masks are washed, it is difficult to completely remove the Si chips from the stencil masks. Therefore, when the stencil mask is used in an electron-beam lithography system, the chips result in charge-up or the like.
Even if an antistatic film is formed on the surface of a stencil mask, a serious problem occurs that the antistatic film is separated due to dirt such as Si chips at a high acceleration voltage.
Moreover, for the existing method of protecting a stencil mask with wax and anisotropically etching it, coating must be repeated many time because the wax is not resistive to a hot anisotropic-etching solution at 70.degree. C. or higher such as KOH aqueous solution or the like. Moreover, because the stencil mask is put in and taken out of the etching solution, a problem occurs that dirt attached on an Si stencil mask cannot completely be removed or a defect is produced on the Si stencil mask, and thereby the product yield is not improved.
Moreover, because an Si.sub.3 N.sub.4 film serving as an inactivation insulating film and silicon substrate are exposed in the case of an existing stencil mask structure, a beam may pass through the film, charge-up may occur, or a stencil mask may be strained by an irradiation beam used due to a difference of stress between support beams of an electron-beam absorbing layer made of Au or the like and Si.sub.3 N.sub.4.